Write text on specific line in a textbox

[2005 user]

I am trying to write text on a specific line in a textbox for example on the forth line)

I've tried :

TextBox1.Lines = TextBox1.Lines.Length

but get this error:

Value of type 'Integer' cannot be converted to '1-dimensional array of String'.

I assume this is beacause TextBox1.Lines is an array of all the text in every line in the textbox.

Multiline is set to true.

How to fix this?